Epigenetic signatures are found in aging linked genes across tissues and different cell types. However, an accurate and reliable epigenetic-aging clock has yet to be discovered. As a potential biomarker for human aging, keratin 19 (k19) is expressed markedly in putative skin stem cell which can be characterized by slow cycling in vivo and progressive decreasing in number from newborn to adult.
We thus isolated the age-specific k19 epigenetic variants from cell-free DNA, spanning the entire human developmental phase. These variants are degenerated at a constant aging rate and can be normalized to age 0 postpartum, defining a full set of high-resolution DNA aging probes. These k19 probe set can be used to differentiate age-related degeneration of the k19 sequence in the skin surface DNA as shown in the age-specific qPCR analysis of an 11 and 12 year-old DNAs after random apurinic crossover hybridization under room temperature.